1. Field of the Invention
This invention relates to a brake control apparatus which can stabilize vehicle behavior when turning.
2. Related Art
Stabilizing vehicle behavior on braking, using, for example anti-skid control, has been known.
This anti-skid control is control wherein the brake hydraulic pressures applied to the wheel cylinders of the wheels are adjusted so that the slip ratios of the wheels fall in a predetermined range during braking caused by depression of a brake pedal. As a result, a braking force is fully exhibited by each of the wheels.
However, there are cases wherein the stabilization of the vehicle behavior is not sufficient with anti-skid control alone. For example, when a brake pedal is depressed during turning, the state of the load acting on the wheels changes. Therefore, by simply carrying out anti-skid control with respect to each wheel, the vehicle behavior is sometimes not stabilized.
That is, as shown in FIG. 1, during turning (for example during left turning), a force rotating the vehicle acts on each wheel according to the balance of longitudinal force (braking force) and side force acting on each wheel. In this case, for example when a left rotating force (an oversteer O/S tendency force) becomes excessive, the vehicle spins. On the other hand, when a right rotating force (an understeer U/S tendency force) becomes excessive, the vehicle drifts.
Also, for example during left turning, normally, the wheel speed of a rear left wheel falls first and its slip ratio increases. Consequently in anti-skid control, pressure-decreasing control is carried out with respect to the rear left wheel. At this time, during left turning, because a large load acts on the front right wheel, the influence of forces at the front right wheel with respect to the vehicle behavior becomes large. Consequently, with simply carrying out pressure-decreasing control with respect to the rear left wheel only, there is the problem that the vehicle behavior becomes unstable.